Process for the production of metal powder



June 30, 1959 G. NAESER ET AL PROCESS FOR THE PRODUCTION OF METAL POWDER 2 Sheets-Sheet 1 Filed March 11, 1955 /nve/7/0rs Ger/70rd Naeser Pefer-Gaeden B y fhe/r afforneys United States Patent FOR THE PRODUCTION OF -METAL POWDER Gerhard Naeser, Duisberg-Huckingen, and Peter Giiden,

Duisberg-Buchholz, Germany, assignors to Mannesmann Aktiengesellschaft, Dusseldorf, Germany, a German company PROCESS The invention relates to a process for the manufacture of metal powder, particularly iron powder, by atomisation of the liquid metal stream by means of water under pressure.

The production of iron and other metal powders is generally carried out on a large technical scale by atomising the molten metal by steam or compressed air. The amount of steam necessary for obtaining fine-grained powder in this way is very high, being about one ton of steam per ton of powder. Consequently, it is necessary to have large steam generators with steam accumulators or heavy compressors which make the process expen- .sive.

In order to develop a less expensive process, it has :already been suggested that the ordinary granulation process for the production of coarse iron granules could be used to produce fine iron powder, using water under ,pressure as the atomising medium. However, this process .has proved not to be suitable for use on a technical scale, since in this way some of the iron is almost completely =oxidised, so that'an iron powder is produced with an .undesirably high average oxygen content. The reason 1 for this is that when the water under pressure impinges on the liquid iron, the liquid iron splutters almost exgplosively in all directions. Consequently, some of the .iron droplets are not cooled sufficiently quickly and consequently are completely or partially oxidised.

The object of the present invention is to eliminate this defect by arranging that the metal particles spraying :in all directions and particularly in an upward direction when atomised by means of water under pressure are cooled so rapidly that no oxidation can take place. According to the invention, this is achieved by supplying the water to the stream of liquid metal in the form of a conical envelope concentrically surrounding the said stream which is preferably directed vertically downwards.

This process has a further advantage that it is possible to vary the nature of the powder produced to a great extent by correlated variations of the water pressure and the cone angle of the water envelope. For example, in order to produce a spattered metal powder, a high water pressure of, for example, 10-30 atmospheres gauge should be employed with a cone angle for the water envelope of about 4-15. n the other hand, a spherical metal powder can he octained by using a lower water pressure of, for example, 3-6 atm. and a cone angle smaller than 4.

The conical formation of the envelope of pressure "water can be produced, by the use of a nozzle with an annular slot for the supply of water under pressure, the said nozzle concentrically surrounding the path of the metal stream.

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In many cases, it is advantageous to atomise the liquid metal stream under a protective gas atmosphere. For this purpose, it is convenient to enclose the metal stream and the aqueous envelope in ,a tube into which the protective gas is introduced. It the atomisation is to take place without a protective gas, such a tube is useful to prevent the liquid metal from being too strongly oxidised by the air.

In order that the invention may be more thoroughly understood an apparatus in accordance with it will be described by way of example with reference to the accompanying drauings in which:

Figure 1 illustrates the production of a spattered metal powder; and

Figure 2 the production of a spherical grain powder.

In the apparatus shown in Figure 1 the envelope 2 of water under pressure issues from the nozzle 1 with the annular slot arranged to give a cone angle of about 10". A liquid metal stream 3 flows into this conical envelope and is atomised when the latter impinges thereon. The droplets which spray in all directions and particularly upwards are carried down by the aqueous envelope of water into the water trough 4, where they are quickly quenched. There is obtained a powder with a uniformly low oxygen content of less than 1% and of spattered grain formation. The metal stream preferably has a thickness of 15 mm. and the gap of the annular nozzle has a width of 1.6 mm. from which the water under pressure flows at a pressure of 22 atm. gauge. The grain size of the irregular powder produced in this manner is smaller than 0.4 mm. A metal tube 5 is provided for the prevention of oxidation or for carrying out the atomisation in a protective gas atmosphere.

In order to produce a powder having a spherical grain formation (see Fig. 2) the aqueous envelope 2 issuing from the annular slotted nozzle 1 is arranged to impinge on the liquid metal stream 3 at a very shallow angle of less than 4. The water pressure used is lower than that used when producing spattered grain powder and is only about half or less for a given grain size. For this purpose, twice as much water is required. Moreover, as shown in Figure 2, the aqueous envelope 2 impinges on the liquid metal stream at the surface of the water in the water trough 4. This provides for contact of the water spray and metal stream just prior to quenching by the water bath.

We claim:

1. A method for making metal powder characterized by the substantial absence of oxidation products, which comprises melting metal, flowing the molten metal in a stream having a diameter on the order of 15 mm., and impinging upon said metal stream a stream of water under pressure, the volume of water in said stream being suflicient to cause substantially complete atomization of said metal stream, said stream of water being in the form of a conical envelope concentrically surrounding said molten metal stream, the angle of impingement being less than about 15 and the pressure of said stream of water being from about 3 to about 30 atmospheres, gauge.

2. The method claimed in claim 1 wherein the metal is iron and the direction of flow of the metal stream is substantially vertical.

3. A method for making metal powder having spherically shaped particles and characterized by the substantial absence of oxidation products, which comprises melting said metal, flowing the molten metal in a stream having a diameter on the order of 15 mm., and imfrom about 3 to about 6 Atmospheres, gauge.

-4. The method claimed in claim B Wherein the metal is iron and the direction of flow' -of the metal stream -is substantially vertical.

References Cited in the file of this patent UNITED STATES PATENTS Rowley Feb. 10,

Seil May 26,

Beamer Apr. 28,

FOREIGN PATENTS France Mar. 2,

Great Britain June 1,

Holland Jan. 15,

Great Britain Nov. 24, 

1. A METHOD FOR MAKING METAL POWDER CHARACTERIZED BY THE SUBSTANTIAL ABSENCE OF OXIDATION PRODUCTS, WHICH COMPRISES MELTING METAL, FLOWING THE MOLTEN METAL IN A STREAM HAVING A DIAMETER ON THE ORDER OF 15 MM, AND IMPINGING UPON SAID METAL STREAM A STREAM OF WATER UNDER PRESSURE, THE VOLUME OF WATER IN SAID STREAM BEING SUFFICIENT TO CAUSE SUBSTANTIALLY COMPLETE ATOMIZATION OF SAID METAL STREAM, SAID STREAM OF WATER BEING IN THE FORM OF A CONICAL ENVELOPE CONCENTRICALLY SURROUNDING SAID MOLTEN METAL STREAM, THE ANGLE OF IMPINGEMENT BEING LESS THAN ABOUT 15* AND THE PRESSURE OF SAID STREAM OF WATER BEING FROM ABOUT 3 TO ABOUT 30 ATMOSPHERES, GUGE. 